head-node: Define Cuirass public URL in Cuirass parameters.

* head-node.scm: Add parameters in Cuirass parameters.

head-node.scm

@@ -541,7 +541,10 @@ CALENDAR, a gexp, and ensures at least FREE-SPACE GiB are available."
                             (cuirass-remote-server-configuration
                              (trigger-url "http://localhost:3000")))
 
-                           (specifications cuirass-specs)))
+                           (specifications cuirass-specs)
+
+                           (parameters (plain-file "cuirass-parameters"
+                                                   "(%cuirass-url \"https://guix.bordeaux.inria.fr\")"))))
 
                  ;; Increase 'max_connections' so Cuirass gets enough.
                  ;; Default is "typically 100" according to